Ductile iron



Feb. 7, 1961 A. P. ALEXANDER ETAL 2,970,902

DUCTILE IRON Filed Jan. 17. 1956 2 Sheets-Sheet 1 250 X Nital & PicralEtch Ifig. 1. Regular Nodular lron 302 brinell.

2 0x Nital & Picfal Etch P 19. 2. Lanthanum treated nodular iron -l97brinell.

25OX Picral 8. Nital Etch Fig. 3. Hard nodular iron 363 brinell.

INVENTORS.

ADOLPH P. ALEXANDER ARTHUR SPENGLERJL Feb. 7, 1961 Filed Jan. 17, 1956Fig. 5.

A. P. ALEXANDER ETAL DUCTILE IRON 2 Sheets-Sheet 2 250 X Picral 8. NitalEtch Fig. 4. Same hard nodular iron as Fig. 3, with 0.010% Lanthanumadded 321 brinell.

Picral 8- Nital Etch Typical structure of beneficiated iron produced byadding percentages of Lanthanum and Magnesium too low for completenodulization.

nvvmmxs AIIOLPH P. ALEXANDER ARTHUR F. SPENGLERJn .Br MQ' ATTK UnitedStates Pat m 2,910,902 nocrnn IRON Adolph P. Alexander and Arthur F.Spengler, In, Memphrs, Tenn., assignors to International HarvesterCompany, a corporation of New Jersey Filed Jan. 17, 1956, Ser. No.559,574

9 Claims (Cl. 75-123) This invention relates to a new and novel ferrousalloy which may be made from any normal base mix composition of grayiron within commonly known specifica tions as well as a base mix of grayiron that is not necessarilywithin the usual range ofsuchspecifications.The resulting ferrous alloy, according to this invention, in the .ascastcondition is soft, ductile, readily machineable and possesses distinctproperties of high tensile strength, high elongation and impact strengthand thereby produces castings which may be machined without thenecessity of a further :thermal treatment.

It is well known that castings made from a normal gray iron mix possessfree carbon in the form of flaked graphite which is more or lessuniformly distributed throughout the matrix resulting in a castinghaving a low tensile strength in the rage of-30,000 to 50,000 pounds persquare inch. It is also well known that if magnesium in amountsnecessary to introduce from the casting or alternatively ceriuminamounts necessary to introduce 0.02 to about 0.050 percent in thecasting,

about 0.02 to 0.04 percent in I or a combination of these two elements,the grap'hitic carbon tends to coalesce or agglomerate to form particleswhich are neither flake-like or spherulitic in shapebut instead areirregularly shaped in whatmay be said 'to be a transition stage betweenthe "flake shape on theone one hand and spheroidal or spherulitic on theother hand.

The particles therefore appear in some portions to reseinble an approachto a flake shape and other portions approach that ofspheroidalorspherulitic shape. Such an iron is generally termedbeneficiated. in that the resulting castings may possess up to and evenexceeding 80,000 pounds per square inch in tensile strength dependingupon the percentage of magnesium or cerium, or a combination of bothelements, is present in the casting.

However, as is well known, when sufiicient. amounts of magnesium (i.e.0.04 to 0.5 percent) or cerium (i.e. 0.05 to 0.5 percent) are added tothe molten base gray iron mix resulting in a casting having, a percentof magnesium or cerium exceeding the maximum percentages specified abovefor beneficiated iron, 'the graphite will essentially coalesce oragglomerate to form nodules of carbon or graphite substantiallyspheroidal orspherulitic in shape which nodules are more or lessdisposed uniformly in the matrix in the casting. Such iron is gener-"ally termed nodular iron and castings made therefrom usually possess atensile strength in the range of90,000

to 120,000 pounds per square inch or higher.

It should be mentioned here that the sulphur content {of the base grayiron mix used for making beneficiated iron ornodular iron, as abovedescribed, must be sufficiently low so that the resulting castingscontains a sul- Well known equation adequately ,defines the aforementioned terms:

pesos herein it will be understood that the following may be further2,970,902 Patented Feb. 7, 1961..

where TC represents the percent total carbon present in present and Sirepresents the percent silicon present. When CE equals 4.30 the iron issaid to be of eutectic composition; when CE exceeds 4.30 the iron issaid to be of hyper-eutectic composition; and when CE is less than 4.30the iron is said to be of hypo-eutectic composition.

Gray irons with nodular graphite made as described above from normalbase irons that conforms with the requirements of the Society forAutomotive Engineers specifications are usually hard and have a Brinell-hardness number (3000 kilogram load-10 millimeter ball) above 250 instandard 1 inch thick Y-lBlock test castings illustrated in MilitarySpecification M1L-l- 17166A (SHIPS). Castings from these irons insections of inch thickness or less are too hard for routine machiningoperations. In addition these light section castings have suflicientfree Or massive iron carbides in the matrix of the cast structure tocause the casting to be brittle with little or noductility. Suchcastings have a low shock resistance and require thermal treatment forsatisfactory engineering use. 7,

Soft as-cast nodular irons can be produced with great difiiculty from acupola with either magnesium or cerium including suitable alloys thereofonly if special precautions are taken. One method is to make a base ironhaving an extremely low silicon content, less than 0.10 percentphosphorus and less than 0.40 percent manganese. Castings made from suchbase iron would be unsuitable for machining operations. base iron mix isadded magnesium or cerium in combination with a high amount of siliconand thereafter a further large addition of a silicon alloy is made, aresulting casting may contain from 2.00 to 4.00 percent silicon whichwould be relatively soft and readily machineable.

For the above reasons it is usualin the foundry industry to use premiumpriced pig iron of carefully selected expensive steel scrap to use forthe production of nodular irons. These requirements for soft as-castnodular iron make it impractical to economically make gray iron from thesame base mix. The only other heretofore known alternative is to makethe hard and brittle type nodular iron castings and subsequentlysubjecting the resulting castings, to a relatively expensive thermaltreatment prior to machining operations. It is therefore a prime objectof this invention to provide beneficiated and nodular irons which in theas-cast condition are soft and ductile, having high strength and shockresistant properties, and may bemade from normal molten base gra'y ironcompositions. 1

It is a further object of this inyention to provide beneficiated andnodular irons which in the as-cast condition are softand ductile, havinghigh strength and shock resistant properties, and may be made from basegray iron molten mixes having compositions outside the limits of normalgray iron specifications.

A still further object of this'invention is to provide beneficiated andnodular irons according to thepreceding objects the properties of thecastings madetherefrom enhanced by a subsequent thermal treat: ment. g

These and other desirablexobjects inherent in and encompassed by theinvention will be more readily understood from the ensuing description,the appended claims and the annexed reproductions of photomicrographswherein: H .1 y

"Figure 1 is a photomicrograph of apolished and etchedsurfaceillustrating hard nodular iron madefrom a northat base gray iron,the microstructure being enlargedjby 250 diameters.

Figure 2 is a photomicmgmph of a Polished and e ged However, if in sucha molten surface illustratingsoft nodular iron made in accordance withthisinvention using the same base gray iron of Fig'-' ure 1, themicrostructure being enlarged by 250 diameters.

Figure 3 is a photo'micrograph of a" polished and etched surfaceillustrating a very hard nodular iron made by the gray ironbeneficiat'ed by the addition of smaller amounts of magnesium andsoftened in accordance with this invention; the microstructure beingenlarged by' 250 dimeters.

The aforementioned military specification indicates that nodular ironhaving a silicon content above 2.50 percent is undesirable. It isunusually'difficult to produce nodular iron in accordance with theaforesaid military specifica'non which is soft in the as-cast conditionfrom a cupola base iron that is also suitable for pouring gray ironcastings conforming to standard engineering specifications because thebase iron silicon content must be kept very low to permit a large lateaddition of ferrosiliconfor so ftening the" resulting castings. Fromthis it may be" readily appreciated that the production of beneficiat'edor nodular gray iron castings. made from normal base" gray iron meetingcommonly known engineering specifications wduld be of exceedingly greatvalue to mercenar industry. Such production would enable a'ifo'undry topour asil inachineable castings hay- P be accomplished by" taking" aladle of moltennormal base gray iron, castings of which would have atensile strength of 30,000 to 50,000 pounds per square inch, and makinga. simple inexpensive ladle addition of specialalloyshereinafte'r"discussed which converts the normal base gray iron tobeneficiated or nodular iron of which castiiigs made therefrom. will besoft, ductile" and of very high tensile strength. a We. have discoveredthat a molten normal base gray iron of .hypoeu tectic" or hyper eutectic c'o rnpo'si tidn, the addition thereto' of amixtu're' of magnesiumfer'rd-silicoii (8.5% Mg 46.0%" .Si)'- plus lanthanum, or, magnesiumferro silicon plus a m ner-ear rare earth: metals containing a minimumof 30% lanthanum will'fres'ult in beneficiate'd or nodularigraphi'teiron depending upon the amountsadded. Thereafter the molten mixisihoculated with a late addition 'of' a. graphitizer such asferro-silicon up to 0.40 percent, and the castings made therefrom assertand machineable and of high strength properti'e's. .Bythis means we haveproduced castings'having' a Brinell hardnessnumber. of about 200' on astandard lr'ensiie strength up to and excee in 90",00q pou-qus squa e"inch. According to our invention this may 7 While that shown in Figure2'wasonly 19'7; A. c'om' 4 I I v The above described results areexceedingly unusual for nodular graphite irons because castings madefrom the same base irons mentioned above but in accordance withpreviously known methods or compositions would result in castingshavinga-Brinnell hardness of over 250 in test bars andlight or thinsection castings could be machined only with 'great'difiiculty if atall.

Referring now to Figures- 1 and'-2- the'se photorn'icro graphsillustrate the structures" of nodular irons made from the same grayi'ronbase mix with the addition of magnesium which formed thesphe'rulitic' or nodular graphite particles. Howeverin thecase of Figure2 the molten iron was in further addition treated with lanthanum inaccordance with our invention. The Brinell hardness of the castingillustrated in Figure 1. was" 302 parison' of the two microstructuresindicatesthatcon; siderable more graphite carbon was freed to formnod-*- ule's when lanthanum was present resultingin a casting having'farmore ferrite in the matrix. Thus it seeiris that the lanthanum reducesthe dissolved carbon or combined carbon to form additional graphitenodules thereby resulting in a softerv casting.

1" Y-Block test bar, with'atensile strength from 80,000

to 100,000 pounds per square inch and dep ending upon the sliconcontent, an elongationof 3 to 10 percent or over, 7

Nodular graphite iron castings made with lanthanum as outlined abovehave a hardness range of from only l. I

rrbm' .110. 01122 as described in ASTM. Designation,

59-49T which covcrsgray irons having tensilelstr engt liv in the rangefrdfn20i000 645,000 pouneg'perisqua're inch.

As a specific example of the above described results we present acomparison of nodular iron; made by a well known procedure, with nodulariron made in accordance with this invention. Four hundred pounds ofbasic cupola normal gray base iron was used. To the first lot of twohundred poundswas added 2.25 percent magnesium ferro silicon (8 .5% Mg,46.0% Si) containing 0.50 percent cerium plus gramsof a high cerium rareearth alloy (Misch-mctalg'see. Table 1'). Then the fir'st l'ot'wa's inoculated with 0.35% ferro-silicon (75% Si) and'pbured into castings.'The second lotwasmade identicallythe same as the first lot?exceptinstead of the high cerium rare earth alloy 75" gramsoffhigli'lanthan'um rare earth alloy" (see Table I) was substituted.Analysis of the.

castings of the first lot indicated about 0:003- percent lanthanumpresent while that of the second lot showed about 0.010 percentlanthanum present.

TABLE 1 Htgh Cerium 1 .High (Misch-Metal), Lanthanum percent 45 45-50%.25 30% (Mini). 15 r 0. v V 20-24%; Fe. 5' 1.0% (Mair.)

Did. Groupof rare earths having atomic numbers 59 to 7l'inclnsive and39in varvinz amounts; A. g i V v "castingsmade from the above mentionedlots were tested for hardness andthe results are shown inTable 2. v p vI TABLE 2 Standard 1", "Y-Blo'c'lc hardfzess of high cerium and high]la'nth zn'um no dula'riiz as-ca'st' condition First Lot" Second Lot 7High Cerium High Lantha- Rare'Ea'rth numRareEmth 1 B rinoll hardness110. (3,000 kg. Lea -rommwbniy.-

'The'Brinell hardness test results of the first lot shown in Table 2 aretypical and are in conformance with the results reported by others.However, theBrinell hardness test results of the second lot areunusually low and llustrates the effect offour invention in softening or-ductilizing the resulting nodular iron. The same type striking resultsarelobtained in the case of beneficiated "-11'01'15 too. In the case ofthe castings from the second flot the microstructures thereof againshowed that far more ferrite (approximately 80% was present than that ofthe castings from the first lot. Furthermore the Brinell hardness of thenodular graphite iron made with the magnesium without the additionofrareearth ma- "terial was over 250. Thus' it can be seen that increas-1 ing amounts of magnesium or ceriumin the castings resultsinprogressive hardening or, "in other words, the presence of cerium ormagnesium in iron castings will result in a harder and more brittleproduct.

The above discussed first example was concerned primarily with acomparison of hardness characteristics of nodular iron made inaccordance with previous known concepts with that of the addition oflanthanum according to our invention.

Table 3 illustrates, in a series of nodular irons made,

from normal base gray irons, the effect of composition on certainphysical properties of the resulting castings made therefrom. It may benoted that the elongation property decreases as the silicon contentincreases wh'le the tensile strength remains fairly constant at from.

I 92,000 to 95,000

pounds per square inch after 2.75% silicon is reached. i

TABLE 3 of high lanthanum rare earths and magnesium Heat N0. 1 2 3 4 5 6SiL, percent 2. 47 2. 51 2. 74 2. 81 3.21 3. 56 percent 3. 44 3. 51 3.53 3. 21 3. 21 2. 82 Mn, percent. 0.41 0.39 0.45 0. 44 0.47 0.45 P,percent 0.05 0.04 0. 04 0.05 0.06 0.08 S, percent. 0.02 0.02 0.02 0.020.02 0.02 Ni, percent 0.12 0.15 0. 31 0. 23 0. 27 0.18 Cr, percent...0.07 0.10 0.13 0.16 0.11 0.17 Mg, percent 0. 045 0.055 0. 043 0.047 0.053 0. 065 Ce, percent" 0.021 u. 026 0.015 0.019 0.022 0. 019 7 La,percent. 0.009 0.011 0. 007 0.008 0.009 0.009 ,BHN -1 197 197 200 207.197 229 Tensile (p. s.1.). 79,500 84,500 92,000 95,000 91,900 92,000Yield (n.s.1.)-..- 61, 200 63,600 81,250 76, 500 66. 450 79, 600Elongation, percent. 10 11 8. 5 7. 0 7.0 3. 0 Unnotched Charpy Impact,Ft. lbs.: 70 F 21.8 19.0 11.0 4.5 40 F 8.3 5.5 5.5 3.0

.1 Broke outside gauge marks.

'A rise in tensile strength to about 80,000 to 95,000

\ pounds'per square inch at constant hardness is rather unusual innodular iron and even in steel. This unusual result seems tobeassociated with the effect of the presence of lanthanum according tothis invention which will be discussed later. It should also be notedfrom Table 3 that the silicon and carbon contents of the several heatsvary considerably but the softening eifect of the lanthanum appears tocontrol the hardness at a low constant. In respect of hardness we havealso no ed a rather amazing phenomena in lanthanum softened nodulariron. We find that light section castings as thick as 04 are softer ascast thanthe standard 1" thick Y-Block corresponding test bar. As anexample we found that using the same iron a Y Block 1" thick eithibiteda hardness of 241 Brinell while a thick 'casting of the'same ironcomposition showed only 217 Brinelll Impact strengthof lanthanum treatednodular irons are also of :a higher order than that of previously known"A s-cast properties of nodular iron produced by additions:

nodular irons. As shown in Table 5 the enhanced impact strength ofnodular irons made in accordance with our invention appears to beindependent of the base composition of the iron or, in other words, thesoftening effect of the lanthanum and its elfect on raising impactstrength of nodular iron is, at least to an appreciable extent,independent of the composition of the base iron which may be of eitherhypo-eutectic or hyper-eutectic composition.

In nodular or beneficiated graphite iron the elongation properties varyinversely with the phosphorus content.

, Therefore the phosphoruscontent should be kept below 0.1 percenttoobtain good elongation properties. It is also preferable to keep thepercentage content of certain other elements such as silicon, manganese,nickel, etc., low in the iron for maximum ductility of the iresultingcasting. However, if special characteristics such as high strength orwear resistance are required, the

nodular or beneficiated iron may be deliberately alloyed in a well knownmanner. In these cases the incorporation of lanthanum of this inventionwill soften the iron and will increase the impact resistance.

The eiIect of thermal treatment" on lanthanum containing nodular ironcastings made according to this invention is illustrated in Table 4 forheat Nos. 3 to '6 of Table No.13.

TABLE 4 Heat treated properties of nodular iron produced by additions ofhigh lanthanum rare earth; and magnesium as in Table 2 i Heat No 3 4 5 6Treatment:

Short Cycle Anneal, 1,700

E. 2% I-Ir.-1,400 F., 2% Hr., Air Coo1 60. 8 12. 5 36. 5 r 34. 0 -40 F15. 8 6.0 11. 0 5. 5 Oil Quench and Temper,

1,725 F., 2% Hrs; Ten1- per, 1,l00 F., 2% Hrs.-

Tensile 151, 000 149, 000 152, 500 122, 000 Yield 119, 000 122, 000 110,500 Elong., 2" 2 5 3.0 3.5 4.0 Hardness, BHN 363 g 363 241 Charpy ImpactF 17. 5 28.0 17.5 40 F 14.0 11.5 16.0 10. 5 Normalize, l,700 F., 2% 1Hrs. Air Oool-- Tensile 114, 500 111, 800 114, 000 109, 250 i :1 90,00091, 750 92,500 85, 250 gm, 2 4.5 3.0 3. 5 5.0 Hardness. BHN 269 302 285269 Charpy Impact:

70 F 16. 5 10.0 14. 5 16. 5 40 F 9. 5 9. 0 S. 5 8. 5

The above results from thermal treatment appear to be well in line withthat which might be reasonably expected.

Although Charpy impact test results apparently do not establish irontoughness as a criterion which ismore thoroughly discussed inDesignation E23-47T of the American Society for Testing Materials,nevertheless we tested some of the nodular iron castings of thisinvention for comparison with nodular irons of the well known type.These impact test results are shown in Table 35.

7 TABLE-5 flmpdctfresillts'on slanda rd 'n'odular iron' and nodular irontreated with lanthanum 1 Gray Iron base treated with magnesium; andsilicon alloy. I 3 Similarbase iron treated with magnesium and siliconalloy plus high lanthanum rare earth alloy. 1

3 Gharpy'unnotched impact as per A.S.T.M. E23-47T. I i 2% hrs, 1700F.2%hrs. 140 O'1*., air cooled total time, shrs. (standard productioncycle). a

As might be expected the impact test results in Table 5 are quitescattered, Thesingle extremely high result for standard nodular iron isnot accounted for nor was it duplicated. Disregarding this extremelyhigh result it appears that the lanthanum treated nodular iron made "inaccordance with this invention may have an average impact strength ofsomewhat higher order than that possessed by nodular iron--made-inaccordance with previously known methods.

As a further demonstration of the softening effect in' the as-castcondition of'=nodulargraphite iron'by' high lanthanumrare-earthscontaining a minimum 'of 30' percent lanthanum, standardnodular iron was first made by the well known addition of magnesiumalloys. The hardness =of-"a standard" 1'' thick Y-Block test bar-casting was 302 'Bn'n'ell. To a 200 pound quantity of the same melt anamount of high lanthanum rare earths was added to incorporate one-fourthounce of lanthanumand the resulting hardness of a 1" thick Y-Block'casting was only 250 Brinell. Then in another similartyp'e'test a veryhard type ofnodular iron was made which resulted i in castings having aBrjinell hardness ofi363 (Figure 3).

Then to 200 pounds of'the iron'melt was added only 8 grams 'of elementallanthanum. --The resulting castings had but 0.010 percentlan'Eihanum'and the Brinell hardness dropped to 321 (Figure 14).

Comparing the microstructuresof the two irons made "in the'lastdescribed test as shown-in Figures '3 and 4,

it will again be noted that the lanthanum containing iron (Figure 4)shows more-carbon in the .form of graphite nodules than-that shown inthe". untreatediron of Figure 3. Again itappears' that the lanthanumte'ndsto free *more carbon 'to' form nodules"antlTcorrespondingly in-{creasing the amount or percentage-of ferrite present in the matrix. Theunderlying causes'and-reasonsfor the formation of nodular graphiteinstead of"flake" graphite in iron is not yet thoroughly understood.Also the reason for the softening eifect'by lanthanum is not completelyclear. As stated previously there is some evidence that lantha-' numfrees an additional amount of carbon to form more graphite nodules andthereby increase the amount of ferrite present in the matrix throughreduction of carbides. It is also suspected that lanthanum softens theiron by 1 combining with gases-such as; hydrogen, oxygen and nitrogenwhich are well known potent iron hardeners.

It has been mentioned previously that the presence of ceriumor magnesiumwill result in a harder gray iron in the as-cast condition. "It shouldalso be noted that under certaincircumstanceslanthanum may be a hardenerfor gray iron. lt hasb'een found" during the course of ourinv'efstigation that if the amount'of lanthanum in the iron exceeds0.020 percent the' 'resiilting'iron will prograssiveiy {becomeharderflas lthe pe centa e of lanthanum further ases. Therefore onlyminute pereefirages offlanthanum-should be used to soften grayiron,namely; the range of 0.004 to 0.020 percent lanthanum, .to softeneither-beneficiated or nodular iron.

As the percentage of magnesium is.lowere'd-:to below 5 about 0.03 or0.04 percent and the lanthanumbelow 0.004 percentcompletespheroidization of the graphite is not achieved and the resultingproduct is -of-the beneficiated iron type. previously discussed. Figure5 represents :a typical structure of beneficiatediron which in 10 l thisillustration has but relatively'few nodules, the bulk of the free carbonbeing coalesced to a transitional stage 'between fiakeform and nodularform. S'uch beneficiated iron is soft having 'a tensile strength in theorder of 00,000 pounds per'square inchrand may haVe -an elongation of upto and even exceeding six percent, For example a beneficiated iron-madein accordance with the above and shown in Figure 5 possessed, in theas-cast condition, a tensile strength of 81,000 pounds per square inchwith ayield strength of 61 ,000pounds per-square 20, inch and anelongation of 4 percent. Such ironmay be used' in numerous applicationswithout the necessity of supplemental thermal treatments.

Having thus described our invention including several specific examplesthereof it can now be seenthat the objects of the invention have beenfully achieved and it must be understood that changes andmodifications-might be made which do not depart from the spirit of the invention; as'disclosed nor from the scope thereof as defined in the appended claims.a Weclaimr; j j k 1. A ductile iron casting having improvedmachinability characteristics containing in the matrix thereof particlesof carbon substantially in' agglomerated form, said castingcontainingfrom 3.00to 3.' 70% total carbon frorn 1.80 to 2.80% 'licon from 0.50 t9-1.00% maiigianelsejfrom 0.10 w02s% phosphorus'fnot more than 0.03%sulfur,

a carbon agglomerant retained 1n anamountsuflicientto agglomeratesubstantially said carbon particles in the ab- -sence of effectiveamounts of retained residual. elements 40 subversive to said'carbonagglomerant, and a-ductilizing agent consisting of metalliolanthanumretained in-an amount of 0.004 to 0.020 percent to impart said improvedniachinability characteristics to said casting inthe as-cast condition.1

2. A ductile iron casting having improved machinability characteristicscontaining in the matrix thereof particles of carbon agglomeratedsubstantially in spheroidal form, said casting containing fr0m'.3.00 to3.70%

total'carbon, from 1.80 to 2.80% silicon, from 0.50: to

1.00% manganese, from 0.10 to 0.25% phosphorusynot more than 0.03%sulfunacarbon agglomerant retained in an amount from 0.0 2 to 0.50%selected from the group of metals consisting of cerium and magnesium inthe absence of eiiective amounts of retained residual elehientssubversive to saidcarbon agglomerant, and a ducparticles of carbonagglomerated substantially in sphe-m roidal form,said casting containingfrom 3.00 to 3.70% total. carbon,.from 1.80 to 12.80% silicon,.from 0.50to 1.00% manganese, from 0.10 to 0.25%'phosphorus, not

more than 0.03% sufur, aretained carboniagglomerantselected from thegroup of metals consisting of'rnagnesium in an amount from 0.04 to 0.5%and cerium in an amount from 0.05 to 0.50% inthe absence of eiiectiveamounts 0 of retained residual element's subversive to saidcaibonagglomerant, and a ductilizing agent consisting of 'metal! lic lanthanumretained in an" amount from 0.004 to0l020 percent to impart saidimproved machinability characters 'istics' tosaid casting in theas-castcondition. as *4. A ductile iron"casting-having im roved-memoir.

was

ty characteristics containing in the matrix thereof particles ofagglomerated graphite shaped irregularly in a transition stage betweenflake form and spheru'itic form, said casting containing from 3.00 to3.70% total carbon, from 1.80 to 2.80% silicon, from 0.50 to 1.00%manganese, from 0.10 to 0.25% phosphorus, not more than 0.03% sulfur, aretained graphite agglomerant selected from the group of metalsconsisting of magnesium in an amount from 0.02 to 0.04% and cerium in anamount from 0.02 to 0.05% in the absence of effective amounts ofretained residual elements subversive to said graphite agglomerant, anda ductilizing agent consisting of metallic lanthanum retained in anamount from 0.004 to 0.020 percent to impart said improved machinabilitycharacteristics to said casting in the as-cast condition.

5. A ductile iron casting having improved machinability characteristicscontaining in the matrix thereof partieles of carbon substantially inagglomerated form, said casting containing from 2.82 to 3.53% totalcarbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, notmore than 0.03% sulfur, a carbon agglomerant retained in an amountsufficient to agglomerate substantially said carbon particles in theabsence of effective amounts of retained residual elements subversive tosaid carbon agg omerant, and a ductilizing agent consisting of metalliclanthanum retained in an amount of 0.004 to 0.020 percent to impart saidimproved machinability characteristics to said casting in the as-castcondition.

6. A ductile iron casting having improved machinability characteristicscontaining in the matrix thereof particles of carbon agglomeratedsubstantially in spheroidal form, said casting containing from 2.82 to3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1%phosphorus, not more than 0.03% sulfur, a carbon agglomerant retained inan amount from 0.02 to 0.50% selected from the group of metalsconsisting of cerium and magnesium in the absence of effective amountsof retained residual elements subversive to said carbon agglomerant, anda ductilizing agent consisting of metallic lanthanum retained in anamount of 0.004 to 0.020% to impart said improved machinabilitycharacteristics to said casting in the as-cast condition.

7. A ductile iron casting having improved machinability characteristicscontaining in the matrix thereof particles of carbon agglomeratedsubstantially in spheroidal form, said casting containing from 2.82 to3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1%phosphorus, not more than 0.03% sulfur, a retained carbon agglomerantselected from the group of metals consisting of magnesium in an amountfrom 0.04 to 0.50% and cerium in an amount from 0.05 to 0.50% in theabsence of effective amounts of retained residual elements subversive tosaid carbon agglomerant, and a ductilizing agent consisting of metalliclanthanum retained in an amount from 0.004 to 0.020 percent to impartsaid improved machinability characteristics to said casitng in theas-cast condition.

8. A ductile iron casting having improved machinabiity characteristicscontaining in the matrix thereof particles'of agglomerated graphiteshaped irregularly in a transition stage between flake form andspherulitic form, said casting containing from 2.82 to 3.53% totalcarbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, notmore than 0.03% sulfur, a' retained graphite agglomerant selected fromthe group of metals consisting of magnesium in an amount from 0.02 to0.04 and cerium in an amount from 0.02 to 0.05% in the absence ofefiective amounts of retained residual elements subversive to saidgraphite agglomerant, and a ductilizing agent consisting of meta liclanthanum retained in an amount from 0.004 to 0.020 percent to impartsaid improved machinability characteristics to said casting in theas-cast condition.

9. A ductile iron casting having improved machinability characteristicscontaining in the matrix thereof particles of carbon agglomeratedsubstantially in spheroidal form, said casting containing from 2.82 to3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1%phosphorus, not more than 0.03% sulfur, a retained carbon agglomerantselected from the group of metals consisting of magnesium in an amountfrom 0.04 to 0.50% and cerium in an amount from 0.05 to 0.50% in theabsence of effective amounts of retained residual elements subversive tosaid carbon agglomerant, and a ductilizing agent consisting of metalliclanthanum retained in an amount from 0.007 to 0.011% to impart saidimproved machinability characteristics to said casting in the as-castcondition.

References Cited in the file of this patent UNITED STATES PATENTS2,622,022 CrOme Dec. 16, 1952 2,841,490 Stevens et a1. July 1, 1958FOREIGN PATENTS 721,717 Great Britain Jan. 12, 1955 730,712 GreatBritain May 25, 1955 1,070,939 France Aug. 19, 1954

2. A DUCTILE IRON CASTING HAVING IMPROVED MACHINABILITY CHARACTERISTICSCONTAINING IN THE MATRIX THEREOF PARTICLES OF CARBON AGGLOMERATEDSUBSTANTIALLY IN SPHEROIDAL FORM, SAID CASTING CONTAINING FROM 3.00 TO3.70% TOTAL CARBON, FROM 1.80 TO 2.80% SILICON, FROM 0.50 TO 1.00%MANGANESE, FROM 0.10 TO 0.25% PHOSPHORUS, NOT MORE THAN 0.03% SULFUR, ACARBON AGGLOMERANT RETAINED IN AN AMOUNT FROM 0.02 TO 0.50% SELECTEDFROM THE GROUP OF METALS CONSISTING OF CERIUM AND MAGNESIUM IN THEABSENCE OF EFFECTIVE AMOUNTS OF RETAINED RESIDUAL ELEMENTS SUBVERSIVE TOSAID CARBON AGGLOMERANT, AND A DUCTILIZING AGENT CONSISTING OF METALLICLANTHANUM RETAINED IN AN AMOUNT OF 0.004 TO 0.020 PERCENT TO IMPART SAIDIMPROVED MACHINABILITY CHARACTERISTICS TO SAID CASTING IN THE AS-CASTCONDITION.